The present invention relates to a sheet registration device and, more particularly, to such a device which receives a sheet at a sheet input, laterally aligns the sheet, and then delivers it to a sheet output. Such devices may find particular application in printing and duplicating systems where sheets of copy paper are sequentially supplied to a printing station. The sheets are typically supplied from a tray containing a stack of sheets. The sheets in the stack are not precisely aligned with respect to the sheet feed mechanism and typically some amount of slippage between the sheets and feed rollers may occur as the sheets are withdrawn from the stack. As a consequence, the sheets may be somewhat misaligned laterally as well as being slightly skewed.
In order to shift a sheet laterally and align the sheet properly, a number of different sheet registration devices have been developed Broadmeyer U.S. Pat. No. 1,728,328 discloses a conveyor including a plurality of bars which support a sheet. A registration surface is positioned to one side of the bars, and the lateral edge of the sheet is urged against this surface. To accomplish this, a series of vacuum rollers which are skewed slightly with respect to the conveyor are positioned along the conveyor. The vacuum rollers translate the sheet along the bars and, at the same time, move it laterally into contact with the registration surface. Since the skewed vacuum rollers provide the sole means of movement of the sheets along the bars, the sheets are continuously urged against the registration surface. As a result, the lateral edge of the sheet may curl upward along the registration surface, producing a sheet which is improperly aligned.
Broadmeyer U.S. Pat. No. 1,728,329 discloses a conveyor having a plurality of moving endless belts and a single vacuum roller which is skewed with respect to the direction of movement of the belt conveyor. The vacuum roller provides lateral movement of a sheet carried by the belt conveyor such that the sheet edge contacts a registration surface.
Providing a belt conveyor as the primary sheet delivery mechanism, with the separate vacuum roller used for lateral alignment, reduces the possibility that the edge of the sheet contacting the registration surface will curl. Nevertheless, the Broadmeyer '329 device provides for application of a lateral shifting force to a sheet for the entire time which it takes the sheet to pass over the vacuum roller. As a consequence, there may still be a tendency for a relatively thin, flexible sheet to be moved too far laterally, past the point at which the lateral edge of the sheet merely contacts the registration surface. Additionally, since a single vacuum roller is used to provide lateral shifting of a sheet, during the times in which the roller engages generally the forward or trailing portions of the sheet, the roller may apply a force to the sheet which tends to rotate it, as well as shift it laterally.
Weisbach U.S. Pat. No. 4,184,673 and Garrett U.S. Pat. No. 2,772,880 both disclose vacuum belt arrangements in which the belts are skewed with respect to the principal direction of movement of a sheet in order to shift the sheet laterally for alignment. The Garrett '880 patent discloses a sheet stacker in which overlapping sheets are shifted laterally into contact with a pair of perpendicular alignment surfaces, while the Weisbach '673 patent discloses a device which shifts each sheet of an overlapping set laterally prior to feeding the sheet to a printer. The angular shifting of the sheets in both of these devices produces a series of overlapping or shingled sheets having two orthogonal edges exposed for abutment against alignment surfaces.
It is seen, therefore, that a relatively simple, reliable sheet alignment device is needed which is capable of receiving a sheet at a sheet input and transporting it to a sheet output, while at the same time aligning the sheet by bringing it into contact with a registration surface. Lateral movement of the sheet into contact with the surface should preferably be provided only for a period of time sufficient to cause such contact to occur.